9 Oct
2007
9 Oct
'07
2:20 a.m.
On 10/9/07, J Blaser <oldcpu2 at rogerwilco.org> wrote:
Yes, you are absolutely correct! The more I think
about it, the more
glad I am to have even this empty chassis. Definitely harder to come by
than the modules that are missing.
Much harder. Boards store flat ;-)
I've come up with a minimum list of boards, and a
wish-list of the
boards that were originally included.
Very handy, but you should still check the backplane - all the list
will show is a snapshot in time - not the final configuration. I've
seen few machines where those labels were updated consistently.
Looks like the the mass storage
was hung off of a UDA50, and some tape devices on the SI 9700 board
That makes sense.
(which I still am completely ignorant of).
I know I went over bits of this before, but perhaps a different
approach might be clearer... Systems Industries made a variety of
disk/tape systems for various DEC machines. I have personally seen
Qbus and 11/750 host cards, and I think there were others (Unibus, at
least). To order an SI system, you'd tell the salesman what box you
had, and what devices you wanted to attach. They would spec out the
right host controller, and the right cards for the SI9900 external box
to do what you wanted to do. I think there was also support for
multiple hosts to access multiple disks - not like a true cluster, but
more like multi-port access between a set of CPUs and a set of disks
and/or tape.
When I used an SI9900, it was nearly as simple as it could be. We had
an SI 9700 board in our 11/750, a pair of 40-pin cables to SI 9900 box
in the next rack, one host-side card in the SI 9900, and two SMD disk
cards in the other half of the SI 9900 box. We had two SMD disks
(60-pin control, 26-pin analog data) in the rack with the SI 9900,
emulating a pair of RM03s and a large RM05. We could have chosen to
hang more disks off our SI 9900, but the way SDI disks were plunging
in price in the late 1980s, we kept the SI 9900 for our boot disk, and
added a couple of RA81s for user data, etc.
In your case, it sounds like the SI 9900 box you would run across (if
it's still on-site to be found), would have one board with a pair of
40-pin connectors that would hang off of your CPU, then one or more
tape interfaces, with, presumably, Pertec-style interfaces.
One of the benefits of the 11/750 over, say, the 11/730, is that the
CMI bus (I think that's what it was called) had really high bandwidth
path to memory. You could hang a low-speed tape drive or two off of
the Unibus, but for the free-standing 125 ips vacuum-column monsters,
I just don't think the Unibus could keep the tape streaming. On our
11/750, we had that SI 9700 for system disk and one data disk, a
UDA-50/RA81 for user directories, and an RH750 and TU78 for backups.
It was hell to keep working, but when the TU78 was up, it *screamed*
through backups.
For your system, since it's going to be easier to find Unibus disk
than an SI 9900, I'd recommend de-installing the SI 9700 (which
involves twiddling the backplane jumpers on that slot to pass grant
across the slot), and picking up a UDA-50.
I have a couple of Fuji SuperEagles and an RA81, so
I'll be on the
lookout for SDI and SMD interfaces for the rebuild. I just hope the
Fujis and RA81 are functional when the time comes!
There were some Emulex Unibus SMD interfaces, but ISTR those were more
common on PDP-11s and VAXen running UNIX, not VMS. Once the RA-81
fell below $20,000, SDI disks became really popular for sites without
VAXclusters.
> Disk drives would have been in another rack I
think.
That's one of the things _I_ would like to do with my 11/750 - mount
an RA70 in the space to the left of the Unibus - where the
battery-backup normally goes... stick a VT102 on top and have a
single-cabinet 11/750 "workstation". :-)
I do already have an 3-bay 8300 set up, so I'd also probably run a
cable over to my RA81 port B, and my MDA 2.3GB ESDI-SDI box, but I'd
like to be able to boot the 11/750 in-cabinet, without spinning up
several amps of external disk.
-ethan